Superoxide dismutases are enzymes which catalyze the decomposition of the superoxide free radical into hydrogen peroxide and molecular oxygen. By scavenging the radical, an obligate and toxic intermediate in the reduction of oxygen, dismutases are indispensable to all organisms with an oxidative metabolism. Two classes of dismutases are known, copper-zinc dismutases, found in the cytoplasms of eukaryotes and bacterial-type dismutases, found in the mitochondria of eukaryotes and in all prokaryotes. The specific aims of this project are to determine the complete amino acid sequence of the copper-zinc dismutase from yeast and the manganese-containing bacterial-type dismutase from Escherichia coli, and that of the mitochondrial dismutases from yeast of chicken liver insofar as possible. In addition, catalytically active fragments from limited chemical and enzymatic proteolysis of dismutases will be sought. Available dismutase sequence data (a) suggest that the two dismutase classes evolved independently in the eukaryote and prokaryote cell lines and (b) provide support for the endosymbiotic origin of mitochondria. The additional sequence data obtained in this project will afford a more rigorous evaluation of those two evolutionary hypotheses. Regions of the dismutase molecule essential for catalytic action will be defined from characterization of active proteolytic fragments and will be identified as highly conserved segments among dismutase sequences. Through such a characterization of the chemical determinants of superoxide dismutase structure and function, insight into the biochemical basis of aerobiosis and oxygen toxicity will be obtained. The superoxide radical has been implicated in the etiology of various disease states, including chemical carcinogenesis, rheumatoid arthritis, and hemolytic anemia. Knowledge of dismutase structure and catalysis will be important for any future therapeutic applications of the enzyme in those syndromes, as a scavenger of the superoxide radical.